804 The Outline of Science 



a terminal. If continuous current from an outside source be sent 

 through the cell, certain interactions take place between the plate 

 chemicals and the electrolyte, and electrical energy is converted 

 into chemical. The cell thus becomes in effect a primary battery 

 willing to reconvert its chemical energy into electrical if the cur- 

 rent be allowed to pass through a circuit in the reverse direction 

 to that of its entry, and the chemicals to revert to their original 

 condition. The amount of energy that can be stored in a cell 

 depends on the size of the plates ; and, while the electrical pressure 

 or voltage of a single cell is strictly limited, any pressure is obtain- 

 able by connecting together in series a sufficient number of cells. 

 In the past storage batteries as a class have suffered from 

 several disadvantages, the most serious of which were their great 

 weight relatively to capacity and the slow rate at which they 

 could safely be charged and discharged. Recently, however, some 

 important improvements have been made, which promise reduc- 

 tions of weight and charging time so great as to give an enormous 

 impetus to the use of the independent accumulator-and-motor 

 vehicle, which has some strong points in its favour, but has 

 hitherto been restricted in radius of action and speed. With the 

 new batteries a journey of 150 miles or more before recharging 

 should be possible, and recharging be a matter of but a few 

 minutes, instead of hours. Even on the railway the new accu- 

 mulator may bring interesting developments. A 90-ton battery 

 is estimated to have a capacity of 8,000 horse-power equivalent 

 to 1,000 horse-power exercised continuously for eight hours. 

 This energy would take a train from London to Edinburgh at 

 express speed. 



Electric Traction 



An electric train or train hauled by an electric locomotive 

 has a great advantage over the ordinary steam train, in that it 

 gets into its stride much more quickly. A steam train starting 



